The purpose of these studies is to determine the role of cell surface IgD in triggering the B cell. In this regard we will (1) attempt to determine the relationship between the structural nature of the antigen and the requirement for IgD vs IgM in trigerring virgin B cells. (2) We will determine mu-predominate (delta minus) B cells can respond to antigens in vitro. (3) We will investigate the relationship between the requirements for IgD on the B cell and the receipt of the T cell signal.